1. Technical Field
The embodiments herein generally relate to communication receiver and, more particularly, to low power receivers reducing implementation complexity in estimation of a Carrier Frequency Offset (CFO) and a Symbol Timing Offset (STO) for spectrally shaped multiple communication standards by eliminating the use of multipliers.
2. Description of the Related Art
Carrier frequency offset (CFO) compensation is a critical issue for receiver design. CFO is mainly caused by a mismatch between a transmitter oscillator and a receiver oscillator. Signal acquisition in coherent demodulation requires convergence of several complex signal processing algorithms, which include symbol timing offset (STO) and carrier frequency offset (CFO) estimation. Power and area reduction is the main concern for low power devices and thus require minimizing implementation complexity involved in STO and CFO estimations.
FIG. 1 illustrates an exploded view of a typical implementation of band extraction. In this typical implementation, low pass filters 102 are used for band extraction for a CFO estimation 104 and a STO estimation 106. An error or precision loss in the low pass filter 102 output will affect the CFO estimation 104 and the STO estimation 106 which lead to inaccurate estimations.
FIG. 2 illustrates an exploded view of a typical implementation of symbol timing offset (STO) estimation based on Godard's method, which adaptively search for a best sampling phase by generating a sampling error by a sampling error generation block 202 using energy maximization followed by a phase lock loop 204. In such an implementation, any loss in precision of estimation will affect final convergence.
Most of the commonly used schemes for STO are more sensitive to CFO or require a carrier frequency to be locked prior to STO estimation. Similarly, low complexity schemes for CFO such as decision directed based carrier recovery methods, are influenced by symbol timing offsets and require symbol synchronization before carrier estimation. All these dependencies lead to a complex implementation, if an effort is made to combine them, to achieve fast signal acquisition.
FIG. 3 illustrates an exploded view of a typical implementation of spectrum shape based carrier frequency offset (CFO) estimation. Here, an upper band edge 302 and a lower band edge 304 are extracted and an energy difference is filtered by a low pass filter 306 to minimize estimation jitter. The carrier frequency offset estimation is proportional to the low pass filter 306 output. Any error that occurs in the low pass filter output 306 will have an impact on the carrier frequency offset (CFO) estimation.
An analog signal chain of the transmitter and receiver can introduce spectrum tilt. This spectrum tilt can influence an accurate estimation of the carrier frequency offset when spectral shape based schemes are used. Spectrum shape based schemes are simple to implement, adaptive in nature, cover a wide range of communication standards, and can be used to estimate CFO and STO concurrently. However, these schemes are highly influenced by spectral tilt impairments, which lead to a totally incorrect estimation in the presence of such impairments.
Most receivers estimate the carrier frequency offset (CFO) and the symbol timing offset (STO) concurrently to avoid dependencies and sensitivity towards each other. For an example, an accurate STO estimation needs to be done before decision directed based CFO estimation schemes. Similarly, a coarse CFO estimation is needed if decision directed schemes are used to estimate STO. Individual efforts have been made to optimize implementation, but have resulted in performance degradation in term of acquisition range and time. Many solutions have been proposed to the problem of CFO estimation, but none of them reduce the complexity of an accurate CFO estimation.